Byounghak Lee

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We describe the design and implementation of KSSOLV, a MATLAB toolbox for solving a class of nonlinear eigenvalue problems known as the <i>Kohn-Sham equations</i>. These types of problems arise in electronic structure calculations, which are nowadays essential for studying the microscopic quantum mechanical properties of molecules, solids, and other(More)
We present a new linearly scaling three-dimensional fragment (LS3DF) method for large scale ab initio electronic structure calculations. LS3DF is based on a divide-and-conquer approach, which incorporates a novel patching scheme that effectively cancels out the artificial boundary effects due to the subdivision of the system. As a consequence, the LS3DF(More)
The mechanical and electrical properties of CdTe tetrapod-shaped nanocrystals have been studied with atomic force microscopy. Tapping mode images of tetrapods deposited on silicon wafers revealed that they contact the surface with three of its arms. The length of these arms was found to be 130+/-10 nm. A large fraction of the tetrapods had a shortened(More)
Another simulation was made, with the circuit simulated in the basic form, without enhancement circuits, assuming G,,,/Gds and CgslCgd ratios of 1000, with the biasing and signal current sources assumed as ideal. This is not realistic for the basic structures, but is reasonable when it is assumed that the additional enhancement circuits are present. The(More)
Three-dimensional topological insulators have protected Dirac-cone surface states. In this Letter we argue that gapped excitonic superfluids with spontaneous coherence between top and bottom surfaces can occur in the topological insulator (TI)-thin-film quantum Hall regime. We find that the large dielectric constants of TI materials increase the layer(More)
The coupling of mechanical and optical properties in semiconductor nanostructures can potentially lead to new types of devices. This work describes our theoretical examination of the mechanical properties of CdSe tetrapods under directional forces, such as may be induced by AFM tips. In addition to studying the general behavior of the mechanical properties(More)
It is widely accepted that low dimensionality of semiconductor heterostructures and nanostructures can significantly improve their thermoelectric efficiency. However, what is less well understood is the precise role of electronic and lattice transport coefficients in the improvement. We differentiate and analyze the electronic and lattice contributions to(More)
Interface morphology dependent Schottky Barrier Height (SBH) and its modulation by substitutional dopants in NiSi<sub>2</sub>/Si interface have been investigated using density functional theory. An accurate band gap of Si was estimated by employing meta-GGA exchange correlation functional. We show that the SBH for electrons (in n-type semiconductor) is(More)
The ROTSE-I experiment has generated CCD photometry for the entire Northern sky in two epochs nightly since March 1998. These sky patrol data are a powerful resource for studies of astrophysical transients. As a demonstration project, we present first results of a search for periodic variable stars derived from ROTSE-I observations. Variable identification,(More)
Purpose: To predict the minimum value of additional material volume for an acceptable preform product. To predict an acceptable preform product without shape defect such as unfilling in a closed-die forging operation. Design/methodology/approach: In order to reduce the number of experiments, an orthogonal array from the Taguchi’s experimental method will be(More)